Previous studies found that cancer patients often have short-term cognitive defects, but little was known about whether these defects persisted or got worse. In a recent Swedish study, reported in the Journal of the National Cancer Institute (June 2005), researchers studied 702 pairs of twins, ages 65 and older, where one twin had a history of cancer and the other did not.

Twin studies control for environmental and genetic factors--genetics plays an important role in cognitive functioning and risk of dementia. Overall, the odds of cognitive dysfunction were two times higher among cancer survivors, and nearly three times higher among long-term cancer survivors, than among their twins. The odds of dementia were also twice as great among cancer survivors.